1) Technical Field of the Invention
The present invention relates to a power semiconductor device incorporating a power semiconductor chip such as an IGBT, MOSFET, and diode.
2) Description of Related Arts
In such a power semiconductor device, electrical connection of the emitter electrode of the IGBT, for example, typically is made through wire-bonding of an aluminum wire, which causes several drawbacks as described below.
Firstly, there is an upper limit for an amount of current that can flow through the thin wire. In order to secure the desired amount of current, the conventional power semiconductor device is designed to have a thicker wire and/or more wires. However, this approach expands the space for wire-bonding, and contradicts the requirement of the device to minimize its size.
Secondly, the thinner wire causes larger impedance. While the thicker wires and more wires in number are adapted for reducing the impedance of the wires, there is still restriction in reducing the impedance as indicated above.
The third drawback is that since current is flows through the interface between the power semiconductor chip and the wire, substantial heat is generated and concentrated at the local area (interface) on the power semiconductor chip. To reduce the concentration of the heat in the conventional art, the area of the interface is extended and/or a plurality of the interfaces are provided at several positions. However, it is difficult to avoid concentration of the heat as thoroughly as desired.
A further problem is that gate oscillation may be caused at an ON-condition of the conventional power semiconductor device. Typically, the power semiconductor chip includes a plurality of cells, each of which has an emitter electrode connected through the wire with a respective one of circuit patterns on an insulating substrate. This structure may lead uneven gate current between the cells at ON-condition, thereby causing breakage or malfunction of the power semiconductor device. Although this problem may be solved by direct connection of each of the cells via wires, the number and areas of bonding-wires have to be increased. Thus, there is still a restriction for eliminating the gate oscillation as the first drawback. In addition, space for connection of wires has to be secured.
While the major drawbacks are described above, there is another issue for radiating heat. According to the conventional power semiconductor device, for example, a base plate is mounted on a radiating fin by means of screws, with grease interposed therebetween, and the heat generated by the semiconductor chip is dissipated only through the radiating fin, of which radiation feature may be insufficient in many cases.
Various power semiconductor devices have been proposed so far, which are disclosed in the Patent Documents as listed below.
Patent Document 1 discloses a power semiconductor device including a signal-system board and a power-system board that are independently produced, and it illustrates a stereoscopic structure in which the control IC chip is mounted on the power IC chip. Patent Document 2 discloses a semiconductor device including a semiconductor chip mounted on an auxiliary board performing a function of a heat sink. According to a power module of Patent Document 3, a semiconductor chip includes an emitter electrode, on which a metal plate having a large surface is mounted for effectively dissipating the heat generated from the semiconductor chip. Patent Document 4 discloses a semiconductor device which effectively radiates the heat from the semiconductor chip through the upper and lower surfaces thereof. Patent Document 5, which has a patent family of U.S. Pat. No. 6,885,096, discloses an IGBT module including the upper and lower external terminals which are connected directly onto the upper and lower electrodes of the IGBT chip, respectively. Also, an insulating layer is provided within the IGBT module for improving insulation. Patent Document 6 provides a power semiconductor module having a spring member for pushing a conductive resin to improve electrical connection of conductive particles within the resin.
Patent Document 1: JP 06-181286, A
Patent Document 2: JP 2000-323630, A
Patent Document 3: JP 2000-068447, A
Patent Document 4: JP 10-056131, A
Patent Document 5: JP 2002-026251, A
Patent Document 6: JP 2000-124398, A
Therefore, the present invention has several purposes including for example, provision of a power semiconductor device, in which the amount of main current is increased while the impedance thereof is reduced, heat is dissipated effectively from the semiconductor chip, and the gate oscillation due to the separation of emitter cells of the semiconductor chip is prevented.